At an oil refinery, crude oil is brought in, generally through a pipeline, at a temperature of approximately 50-70° F. Before the crude oil enters a crude heater, the crude is pre-heated to a desired temperature to optimize the performance of the crude heater and reduce fuel costs. Once the crude oil is pre-heated to a desired temperature of nominally 400° F., it enters a flash drum or flash tower, wherein the lighter hydrocarbons (such as butane, propane and gasoline) are removed from the crude oil by evaporation or flashing. The remaining crude oil is then transferred to the crude heater for further heating prior to separation in the crude tower.
The final products produced (naphtha, diesel fuel, gasoline, asphalt, etc.) must be cooled before being transported to storage. One method of cooling passes the product through heat exchange equipment, whereby the temperature of the finished product is cooled and the temperature of the crude oil is increased. Any number of heat exchangers can be utilized to reach the desired temperature of the crude, and to reduce the temperature of the product. A furnace is then utilized to further heat the crude oil prior to entering the crude tower for fractionation. To increase efficiency of this heat exchange process it is common for refineries to utilize a flash drum or flash tower that is installed mid-way through the heat exchange process. This equipment allows light hydrocarbons, and contaminants such as water, to flash or be released from the oil, as further heating of this material is not required. The removal, by flashing, of the light material and contaminants increases the efficiency of the further heat exchanging equipment and furnace.
It is well known that fouling in the preheat circuit, progressively worsens as the crude temperature increases, cumulating with the most extensive fouling being observed in the crude heater. Fouling has also been observed in kerosene sections of the crude tower with excessive levels of phosphorus not normally expected nor historically observed in the foulants. Samples of the coke obtained from the pre-heat exchangers and crude heaters indicate these elevated levels of phosphorus. Phosphorus is known to reduce corrosion. Chemicals containing Phosphorous are understood to be found in the production or transportation of certain types of crude oils. It is believed that the elevated levels of phosphorus are contributing to the excessive fouling observed in the preheat exchanger circuits and crude heaters.
The removal of the additional contaminants and light hydrocarbons, specifically kerosene at the flash tower or flash drum, results in lower phosphorus levels downstream in the crude heater and other vessels. This reduction in phosphorus has been shown to decrease unwanted fouling in downstream vessels.
This reduction in light hydrocarbons reduces the phosphorus found in the crude thereby reducing fouling in the crude heater and downstream vessels.